1. Field of the Invention
The present invention relates to an electrolysis apparatus having a porous electrical conductor for use as an electrolysis power feeding element, an electrochemical reaction membrane apparatus having a porous electrical conductor provided at least on one surface of a membrane used in an electrochemical reaction, and the porous electrical conductor used in these apparatuses. Further, the present invention relates to a method of producing the porous electrical conductor.
2. Description of the Related Art
In recent years, systems for supplying electrical power using hydrogen as a fuel have been proposed. For example, a polymer electrolyte fuel cell is known. The polymer electrolyte fuel cell includes a membrane electrode assembly and separators sandwiching the membrane electrode assembly. The membrane electrode assembly includes an anode, a cathode, and a solid polymer electrolyte membrane (ion exchange membrane) interposed between the anode and the cathode. Each of the anode and the cathode has an electrode catalyst layer and a gas diffusion layer.
In the fuel cell, a fuel gas such as a gas chiefly containing hydrogen (hereinafter also referred to as the “hydrogen-containing gas”) is supplied to the anode. A gas chiefly containing oxygen or the air (hereinafter also referred to as the “oxygen-containing gas”) is supplied to the cathode. The catalyst of the anode induces a chemical reaction of the fuel gas to split the hydrogen molecule into hydrogen ions and electrons. The hydrogen ions move toward the cathode through the electrolyte membrane, and the electrons flow through an external circuit to the cathode, creating DC electrical energy.
In general, a water electrolysis apparatus is adopted for producing hydrogen as a fuel. The water electrolysis apparatus uses a solid polymer electrolyte membrane for decomposing water to produce hydrogen (and oxygen). Electrode catalyst layers are provided on both surfaces of the solid polymer electrolyte membrane to form a membrane electrode assembly. Power feeding elements are provided on both surfaces of the membrane electrode assembly to form a unit of the water electrolysis apparatus. That is, the unit of the water electrolysis apparatus substantially has the same structure as the fuel cell.
After a plurality of units are stacked together, the voltage is applied to the opposite ends in the stacking direction. Water is supplied to the anode side power feeding element. Therefore, the water is decomposed into hydrogen ions (protons) at the anode of the membrane electrode assembly. The hydrogen ions pass through the solid polymer electrolyte membrane toward the cathode. The hydrogen ions combine with electrons to produce hydrogen. Further, at the anode, oxygen is produced together with the hydrogen ion. The oxygen and the redundant water are discharged from the unit.
For example, the power feeding element is made of a porous electrical conductive plate as disclosed in Japanese Laid-Open Patent Publication No. 2004-71456. In the conventional technique, as shown in FIG. 10, spherical gas atomized titanium powder 1 having a predetermined grain size is filled in a high density alumina sintering container 2 without any pressurization. Then, the spherical gas atomized titanium powder 1 filled in the container 2 is vacuum sintered without any pressurization to produce a sintered body of titanium powder having a plate shape. One surface of the sintered body of titanium powder is smoothened by a grinding process or a cutting process, and the one surface contacts a membrane electrode assembly (not shown).
In the conventional technique, for example, as shown in FIG. 11, when a surface 3a of a sintered body 3 of titanium powder is subjected to the grinding process or the cutting process, at the time of grinding or cutting, deformed portions 4 are likely to be formed. Thus, the porosity in the surface 3a of the sintered body 3 of titanium powder may be decreased undesirably. If the porosity in the surface 3a is decreased, the pressure loss in fluid is increased significantly. Therefore, at the time of water electrolysis, the oxygen produced on the surface of the anode electrolyte layer of the membrane electrode assembly cannot enter the anode side power feeding element. Consequently, the oxygen is retained between the anode catalyst layer and the power feeding element.
Thus, water supply becomes difficult. The water electrolysis is not performed desirably, and the moisture of the solid polymer electrolyte membrane is not maintained. The membrane resistance is increased, and the electrolysis voltage becomes high.